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The research aimed to investigate the bioremediation of spent engine oil on selected contaminated soils within Ilorin metropolis. To achieve this, soil samples were collected from three (3) mechanic workshops along Taiwo axis within the metropolis. The soil samples were then subjected to bioremediation using the land-farming approach. The physicochemical parameters of the soil samples before and after bioremediation were analyzed using standard methods. Bacteria were isolated using standard procedures and identified using biochemical tests and molecular methods. Results for the physicochemical parameters of the soil samples before bioremediation include particle size (all sandy in nature); pH (6.00 ± 0.14 - 6.20 ± 0.14); Organic carbon (14.65 ± 3.20 - 17.54 ± 1.87), Organic matter (33.50 ± 0.85 - 43.45 ± 9.12) and heavy metals (ND - 11.74 ± 0.07). Values after bioremediation for pH, organic carbon, organic matter and heavy metals were 8.25 ± 0.07 - 8.90 ± 0.14, 13.07 ± 0.05 - 13.25 ± 0.84, 37.25 ± 1.06 - 44.80 ± 1.13, ND - 9.40 ± 0.04 respectively. Values for bacterial count before and after bioremediation of the soil samples were 8.00  1.41 - 67.50 ± 2.12 x 105 CFU/mL and 6.50 ± 2.12 - 164.00 ± 11.31 x 105 CFU/mL respectively. Bacterial isolates were identified as Pseudomonas sp., Enterobacter sp., Acinetobacter sp., and Bacillus sp. while the hydrocarbon-utilizing bacteria were identified as Thalassospira mesophila strain JCM 18969; Pseudomonas fluorescens F113; Siccibacter turicensis LMG 23730; Pseudomonas Zeshuii strain KACC 15471; Pseudomonas stutzeri strain CGMCC 1.1803 and Marinobacter hydrocarbonoclasticus strain ATCC 49840. In conclusion, the bacteria isolates effectively bioremediated the spent engine oil contaminated soils with a reduction of hydrocarbon pollutants.

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